In recent years, the increasing demand for electric vehicles, digital devices such as PCs and smartphones, and renewable energy storage systems has created a need for higher-performance batteries. Accordingly, the thermal conductivity of the case that houses the battery is becoming increasingly important. In this study, compositions with high thermal conductivity and good castability were investigated, focusing on Mg-Al-Ca alloys, and the relationship between the two was examined through thermal conductivity measurements and microstructural observations. As a result, the Mg-6%Al-4%Ca alloy was optimal in terms of castability and thermal conductivity. It was confirmed that a lower Al solid solution capacity and a higher purity of the matrix phase are important to improve the thermal conductivity. It is also suggested that the second phase, platelet Al₂Ca, is likely to be recognized and enriched in the matrix, contributing to the improvement of thermal conductivity. The amount of Ca solid solution in the matrix was suggested to be reduced by the enrichment of Al in the matrix. The Ca solid solution in the matrix was found to be less effective in reducing thermal conductivity than the Al solid solution.

The potential for magnesium storage batteries to become the next generation of rechargeable batteries is high. This is largely due to the abundance of magnesium metal resources and their high safety and electric capacity per volume. Our research team has been studying magnesium alloys as anode materials for these batteries. Specifically, we have been investigating the electrochemical activity and mechanism of adding copper to Mg-9mass%Al and Mg- 9mass%Al-3mass%Ca. Our findings indicate that the electrochemical activity increased with the addition of 1mass%Cu, but decreased with the addition of 3mass%Cu. In addition, changes in lattice constant and basal orientation were also observed. These changes decreased with 1mass%Cu and increased with 3mass%Cu. SEM observations showed that the cell delimitation was indistinct for the 1%Cu addition.

We subjected an A5052 aluminum alloy sample to a dry and rapid surface treatment using 355-nm pulsed laser irradiation, and measured the effects of surface modification. We varied the laser irradiation pitch and found the processed surfaces to have an irregular and complicated topography up to a depth of about 5 μm. X-ray photoelectron spectroscopy (XPS) analysis of the material surfaces revealed that Al₂O₃ with a binding energy of 74 eV was formed regardless of laser irradiation, and that increased irradiation density accelerates surface oxidation. While the non-laser-irradiated areas exhibited hydrophobicity, laser-irradiated regions became superhydrophilic with a contact angle of less than 5°. We performed tensile shear tests on lap joint specimens produced at a beam scanning speed of 500 mm/s and a laser irradiation pitch of 5 μm, and obtained a joint strength of 10 MPa. These results indicate that UV pulsed laser irradiation is effective for fast surface modification.

The changes in hardness and Young’s modulus of an AZ91D alloy during aging were measured to investigate the relationship between these mechanical properties and the volume fraction of the precipitates. The hardness and Young’s modulus of the alloy increased with aging. In the early stage of aging, discontinuous precipitation (DP) of the cellular precipitates having lamellar structure of Mg₁₇Al₁₂ (β) and Mg phases occurred in the vicinity of grain boundaries. After further aging time, the volume fraction of β phase increased rapidly as the DP area expanded and the continuous precipitation (CP) of the β phase began to occur in the interior of grains. The volume fraction of β phase in the DP region as well as the hardness of the DP region remained unchanged during aging. In contrast, the hardness of the CP region increased during aging with increasing the volume fraction of β phase in the CP region. Young’s modulus increased with the volume fraction of β phases, showing changes close to those predicted by the rule of mixtures. In addition, a simple analysis indicated that the β phase in the DP region was more effective in improving the elastic modulus than that in the CP region.

Pure magnesium (Mg) powders added 0.50 g of stearic acid were mechanically milled (MMed) using a vibration ball mill. The MMed powders were consolidated into bulk materials by the spark plasma sintering (SPS). Changes in hardness, solid-state reactions, thickness and internal structure of the SPS materials have been examined by hardness measurements, X-ray diffraction (XRD), vernier caliper and X-ray computed tomography (CT), respectively. The hardness of the SPS materials decreased with increasing sintering pressure and temperature. Minimum value of Vickers hardness was 17 HV. The formation of MgH₂ by solid-state reaction was observed during sintering. The maximum thickness of the SPS materials was 10.4 mm, and this value was a 46% increase compared to that of the MM 0 h thickness. The thickness of the SPS materials increased with increasing sintering temperature. No effect of sintering holding time on thickness of the SPS materials was observed. X-ray CT images showed that the pores of the SPS materials were generated in a flattened shape. The SPS materials densified up to 723 K, but expanded above 723 K during sintering.